Plant seed oils, such as palm oil, sunflower oil and rapeseed (Canola) oil, are a major agricultural commodity worldwide with a large variety of industrial and nutritional uses. More than 15 billion pounds of plant seed oil are produced annually in the United States alone. Wallis J., et al., “Seed oils and their metabolic engineering,” in: SEED TECHNOLOGY AND ITS BIOLOGICAL BASIS, M. Black & J. D. Bewley (eds.), Sheffield Biological Sciences (2000). Ninety eight percent of the plant seed oil production in the United States is used is for nutritional purposes, such as in the manufacture of cooking oil and margarine. The balance of plant oils are used as raw materials in the manufacture of industrial products such as soaps, plasticizers, polymers, surfactants and lubricants.
Plant oils are triacylglycerols, i.e., a glycerol moiety in which each of the hydroxyl groups is esterified to a fatty acid. The glycerol backbone of the triacyl glycerol is invariable in structure, but the fatty acids attached to the glycerol vary considerably depending on the plant oil.
The structure of the fatty acid determines the physical and chemical properties of the plant oil. For example, the number of double bonds in a fatty acid, a variable frequently referred to as the “degree of unsaturation,” affects the melting point of oils, while the chain length of a fatty acid affects its viscosity, lubricity and solubility.
Triacylglycerol molecules are insoluble in aqueous environments and tend to coalesce into oil droplets. In order to store these water insoluble triacylglycerols, plants have developed unique seed oil storage compartments of approximately 1-10 μm in diameter within the plant seed cells, variously known as “oil bodies,” “oleosomes,” “lipid bodies,” and “spherosomes” (collectively, “oleosomes”). See Huang, Ann. Rev. Plant Mol. Biol. 43: 177-200 (1992). In addition to plant oil, these oleosomes comprise two chemical constituents: phospholipids and a class of proteins, known to the art as oil body proteins. From a structural standpoint, oleosomes are a triacylglycerol core encapsulated by a half unit membrane of phospholipids, in which the oil body proteins are embedded. Oil body proteins are believed to play a role in preventing the oleosomes from coalescing into much larger oil droplets.
For extraction of extract plant oils, the seeds are crushed or pressed and then refined using processes typically involving the use of organic solvents to separate the plant oil from other seed constituents, such as seed proteins and carbohydrates. Non-organic solvent-based plant oil extraction methodologies also have been developed, as described, for example, by Embong and Jelen, Can. Inst. Food Sci. Techn. J. 10: 239-43 (1977).
Since the primary objective of these extraction processes is to obtain pure plant oil, however, they typically disrupt oleosome structural. Thus, conventional compositions prepared from plant oils generally do not comprise intact oleosomes.
For instance, U.S. Pat. No. 5,683,740 and No. 5,613,583 to Voultoury et al. disclose emulsions prepared from crushed seeds of oleaginous plants comprising lipidic vesicles. In the course of the crushing process described in these patents, the oleosomes substantially lose their structural integrity. Accordingly, it is disclosed that in the crushing process 70% to 90% of the seed oil is released in the form of free oil.
On the other hand, oleosomes that are isolated from plant seeds in a structurally intact form have a recognized, practical utility. Notably, oleosomes permit the formulation of complex mixtures of aqueous compounds and oil, in the absence of exogenous emulsifiers, at room temperature, see PCT Application 2005/097059 to Guth et al., and oleosomes may be loaded with active ingredients, as described by Murray et al., PCT Application 2005/030169.
A non-destructive methodology for preparing oleosomes is disclosed by Deckers et al. in U.S. Pat. No. 6,146,645, U.S. Pat. No. 6,183,762, U.S. Pat. No. 6,210,742, No. 6,372,234, U.S. Pat. No. 6,582,710, U.S. Pat. No. 6,596,287, U.S. Pat. No. 6,599,513 and No. 6,761,914 (collectively, the “Deckers Patents”). In accordance with the Deckers Patents, a purified oleosome preparation may be obtained and used to prepare emulsions in the presence of a multiplicity of other substances, in order to achieve a desirable balance of emulsification, viscosity and appearance and render these emulsions suitable for cosmetic, food, pharmaceutical, and industrial applications, inter alia.
PCT applications 2007/122421 and 2007/122422 to Gray et al. and Galley et al., respectively, relate an oleosome-containing composition for formulation and administration to a mammal. The disclosed oleosome composition, termed the “oil curd,” may be prepared from oleaginous plants and grains, and it additionally comprises extrinsic plant material, such as plant seed proteins including albumins, globulins, prolamines and glutelins, and carbohydrates. The latter, according to application 2007/122421, impart certain desirable properties, such as enhanced emulsion stability and compatibility with certain chemicals, notably detergents.
For practical applications, an oleosome preparation preferably does not undergo undesirable physical or chemical changes when various conditions may pertain, as during prolonged storage, when the oleosome preparation undergoes temperature fluctuations, as commonly occurs during transport, or when the oleosome preparation is used as an ingredient in formulation processes that may involve the use of shear forces, heating and cooling steps or the addition of reactive chemical agents. Of particular concern in this last regard are biological agents such as bacteria, fungi, mycoplasmas and the like, since their exposure to oil body preparations may well cause degradation of the oleosomes.
In order to protect oleosomes from the exposure to biological agents, preservatives may be added to oleosome preparations. Yet safety concerns and chemical reactivity/interaction with the oleosome protein coat disqualify many well-known preservatives, such as quaternary ammonium salts, formaldehyde releasing compounds, chlorinated compounds and phthalates, from use in food applications or in cosmetics, skin care, topical pharmaceutical applications, and the like. Accordingly, the most widely accepted and desirable preservatives for these applications are acid salts, such as benzoates, salicylates, sorbates, propionates, and acids such as dehydroacetic acid and ferulic acid.
In order to act as preservatives, acid or acid salt preservative agents must be substantially in their acid form, i.e., at a pH of less than 6.0 and preferably between 4.0 and 5.0. However, the present inventors have observed that, within this acidic pH range, an oleosome preparation lacks physical stability, in the sense that oleosome structure is weakened and oil “leaks” from the oleosomes; hence, it becomes problematic to mix in other ingredients, thereby to prepare a finished formulation comprised of intact oleosomes.
This problem is especially acute when oleosomes are introduced into skin care products, which frequently are formulated for compatibility with human skin, for which the pH ranges between 4.1 and 5.8. See Segger, et al., IFSCC 10: 2 (2007). Some topical products, such as skin exfoliants that contain acids like lactic acid, glycolic acids and salicylic acid, have an even lower pH, in a range of 3.5 and 4.5, which is far below the value at which oleosomes generally are stable physically.
In the presence of monohydric alcohols, moreover, oleosome structure is weakened, the present inventors have observed, resulting in oil leakage from the oleosome. Consequently, typical oleosome preparations are not physically stable in products, such as hand sanitizers, that require high levels of a monohydric alcohol.
To an oleosome preparation, according to the Deckers Patents, Glydant Plus®, Phenonip®, methylparaben, propylparaben, Germall 115®, Germaben II®, phytic acid and mixtures thereof may be added in order to achieve stability in the presence of bacteria, fungi, and other biological agents. The Deckers Patents do not specify the impact of these agents on the physical integrity of the constituent oleosome preparation, however.
In summary, there are shortcomings in conventional methods for manufacturing oleosome preparations. In particular, there is a need for improved methodology to stabilize oleosome preparations against undesirable physical or chemical changes that otherwise occur under a variety of conditions. Pursuant to conventional practice, it is unclear whether and how an oleosome preparation may be obtained that is preserved from a microbial standpoint and that is stable with respect to physical aspects of a preparation in an acidic pH range and in the presence of high levels of monohydric alcohol, as discussed above.